The present invention relates to a discharge lamp apparatus, and particularly relates to a discharge lamp apparatus in which an arc tube, in the form of a discharge lamp body having opposed discharge electrodes received in an enclosed glass bulb, is supported by a lead support projecting from an insulating base made of synthetic resin.
As shown in FIG. 4, a discharge lamp apparatus of the same general type to which the invention relates includes a pair of metal lead supports 2 and 3, which act as current paths, projecting from an insulating base 1 made of synthetic resin, and an arc tube 4, which is a discharge lamp body, supported by the lead supports 2 and 3. The arc tube 4 has a sealed glass bulb 4a in which electrodes 5 are provided in opposition to each other. Lead wires 6a and 6b are electrically connected to the respective electrodes 5, and are connected to metal supports 7a and 7b, which are fixed to the respective lead supports 2 and 3. The lead supports 2 and 3 are respectively integrally welded to metal connector terminals 8a and 8b projecting outward from the rear side of the base 1. The lead support 2, which is integrated with the terminal 8a and insert-molded in the base 1, is coated with a covering portion 1a projecting from the base 1. The covering portion 1a is further covered with an insulating cylindrical body 9 made of ceramic, thereby ensuring good insulation properties from the terminal 8b side current path constituted by the lead support 3, the metal support 7b, and the lead wire 6b.
Reference numeral 9a designates a push-on type stopper for fixing the insulating cylindrical body 9 to the lead support 2. Reference numeral 1b designates a flange-like focusing ring formed on the base 1. The electrodes 5 are arranged in predetermined positions with respect to the focusing ring 1b. Reference symbol G designates an ultraviolet-ray shielding globe for cutting from the rays emitted by the arc tube ultraviolet rays within wavelengths harmful to health.
However, the discharge lamp apparatus described above has a problem in that the temperature of the arc tube 4 becomes so high that the covering portion 1a formed on the outer circumference of the lead support 2 is affected by the heat to thereby change its quality such that the dielectric strength at the covering portion 1a is lowered. Thus, the service life of the covering portion 1a is not sufficiently long. In the case in which the electrode 5 is set at a position shifted toward the lead support 2a, as particularly indicated by reference numeral 5a in FIG. 4, the quality of the covering portion 1a is even more strongly affected.
Further, in the conventional discharge lamp apparatus, the insulating cylindrical body 9 is fitted onto the lead support 2 and fixed by use of the push-on stopper 9a or the like so that the cylindrical body 9 cannot come off the lead support 2. This makes the assembling process of the discharge lamp apparatus troublesome.